1. Field of the Invention
The invention relates to a method and equipment for producing fatty acid methyl ester, more particularly diesel fuel for vehicles, whereby saturated and unsaturated higher fatty substances of vegetable and/or animal origin are compounded with a potent alkaline solution, particularly a potassium solution, and dissolved in alcohol, particularly methanol, and the two components reach a chemical balance state through emulsification of the mixture in a reaction section with a phase separation section, whereby the fats are transesterified into fatty acid methyl ester, and on reaching the chemical balance state the residues such as triglycerides, glycerine, soap, non-transesterified fats, etc. are separated from the fatty acid methyl ester.
2. Discussion of Background
Such methods are known, whereby the alkaline solution compounded in alcohol is mixed in a mixing tank with the fat or oil for about 20 minutes up to 1 hour. After mixing, the mixture is left to stand. This sedimentation process takes approx. 5–8 hours. After sedimentation, the glycerine phase is removed. Then the liquid phase is again compounded with methanol potassium alkaline solution, if necessary, and the process of mixing and removal is repeated. The transesterified liquid is then neutralized with phosphoric acid, citric acid or other acids, whereby soap and the potassium salts of the acids are sedimented. In some cases, it is rinsed with water, whereby the water absorbs the soap, potassium solution, etc. This phase is also removed. Subsequently, all kinds of cleaning steps are possible. The process of stripping is also possible, whereby air flows in a counterflow to the ester in a scrubbing tower. The disadvantage of this process, which is based on a low-pressure transesterification process, is the long production time. Apart from the mixing process, long standing times are also required in the sedimentation phases. Moreover, the containers require a lot of space. The high static cost of heavy construction and foundations is a further disadvantage.
Another disadvantage of the known method is the fact that there is always more or less contamination of the fuel.
From Falbe and Regitz, RÖMPP Chemie Lexikon, 9th Edition, Vol. 2, Georg Thieme Verlag Stuttgart-New York 1990, page 1343, a method for the production of fatty acid methyl ester is known, wherein distillation is carried out after sedimentation of the glycerine solution in a separator, in order to purify and fractionate the methyl ester if required. Moreover, the reaction rate of the transesterification can be accelerated by increasing the temperature and with the help of alkaline or acid catalysts. The disadvantage of this method is the fact that the precipitation phase of the glycerine solution in the separator and even the possibility to accelerate the reaction time does not shorten the production time notably compared with the above state of the art.
Moreover, AT-PS 398 777 contains a method for the cleaning of raw vegetable oil esters, whereby the vegetable oil ester is obtained by alkaline transesterification. The transesterification takes place with methanol in excess, with the addition of potassium hydroxide as a catalyst. The raw vegetable oil ester is treated with water vapor, whereby a glycerine phase is produced, which is removed. In this process, intensive mixing is required for transesterification, and the distilled alcohol can be recycled after recovery in a distillation column.
However, other methods based on a high-pressure transesterification process are also known. Thereby, transesterification takes place in an autoclave with a relatively short reaction time. The disadvantage of such methods or equipment lies in the fact that an economic production of fatty acid methyl ester, for example for diesel fuel for vehicles, is absolutely impossible.
Moreover, the transesterification process in two steps is also known. Thereby, the yield in terms of quantity and quality is certainly higher than with transesterification in one step, but again economic efficiency is not possible due to the high plant and production costs.